Electrical isolation between a current sensing and measurement system and an electrical circuit that contains the sampled current is an important consideration in the design and implementation of current sensing and measurement systems. Ideally, a current sensing and measurement system should not affect the operation of the circuit that contains the sampled current by removing current, i.e., the current measurement system should have a nearly zero insertion loss. In addition, the current sensing and measurement system should not inject electrical noise or other interfering signals into either the sampled current or other components and currents within the circuit or other nearby circuits. The current sensing and measurement system should also have a well defined, e.g., linear, relationship between the measured current and the output signal provided by the current sensing and measurement system over the expected range of currents. For measuring currents within integrated circuits, the current sensor should also be easily integrated onto the integrated circuit.
Typically, prior art current measurement systems rely upon a resistance sensor that converts the measured current into a sensed voltage signal and provides the voltage signal to a high impedance sensing front end amplifier that is used to condition the sensed voltage signal. The conditioned signal is transmitted across an isolating barrier using magnetic, capacitive, or optical transmission means. These prior art techniques, however, require the transmission of power backward across the isolating barrier to bias the high impedance sensing front end amplifier and to provide any necessary power to the magnetic, capacitive, or optical transmission means. In other prior art current sensing and measurement systems, Hall effect sensors, magneto-resistive devices, and flux gate devices are used to isolate the sampled current and provide an output signal indicative of the measured current.
Because these prior art devices required power to be transferred in the reverse direction across the barrier to bias and power the front end devices, noise or interfering signals can be introduced into the measured current, the circuit containing the measured current, or other nearby circuits or components. Also, these prior art methods may introduce a significant insertion loss to the circuit containing the sampled current due to the resistance used to sample the current. Furthermore, Hall effect sensors, flux gate devices, and magneto resistive devices are not easily integrated onto an integrated circuit and, through the presence of the magnetic fields that are required for their operation, these devices can interfere with other devices and circuits on the integrated circuit or that are physically proximate thereto. Some of these magnetic based systems also may have poor linearity over the expected range of currents.
Therefore, it would be advantageous to provide a current sensor for an integrated circuit that provides for low insertion loss, has high isolation, that has a well defined relationship over the expected range of current, is easily placed on an integrated circuit, and does not inject noise or interfering signals into the other devices on the integrated circuit.
A current sensor and a method for measuring currents on an integrated circuit that uses a thermal difference generator that generates a first temperature at a temperature generating junction and a second temperature at a second temperature generating junction, where the two temperature generating junctions are spaced apart from one another, where the temperature difference between the first and second temperatures is a function of the sampled current. A thermal difference detector has a first temperature sensing junction thermally coupled to the first temperature generating junction and a second temperature sensing junction thermally coupled to the second temperature generating junction. The thermal difference detector detects the temperature difference between the first and second temperature sensing junctions and provides a measurement signal that is indicative of the temperature difference between the two temperature sensing junctions. The temperature difference being indicative of the sampled current.
In one embodiment, the current sensor is formed on a silicon die and includes a first thermal difference generator that has a current input portion consisting of a first conductive material physically coupled to a current transfer portion consisting of a second conductive material dissimilar to the first conductive material. The current input portion and the current transfer portion are joined together and form a first temperature generating junction. The current transfer portion is coupled to a current output portion consisting of the first conductive material and forming a second temperature generating junction therewith. The sampled current is coupled to the current input portion, flows through the first temperature generating junction, across the current transfer portion, through the second temperature generating junction and is provided at the current output portion without significant loss. The current flowing through the first thermal difference generator results in the first thermal difference generator generating a first temperature at the first temperature generating junction and a second temperature at the second temperature generating junction, the first temperature being less than the second temperature.
The current sensor further includes a first thermal difference sensor. The first thermal difference sensor includes a first output portion consisting of a third conductive material that is physically coupled to a current transfer portion consisting of a fourth conductive material that is dissimilar to the third conductive material. The first output portion and the current transfer portion join together to form a first temperature sensing junction. A second output portion consisting of the third conductive material is physically coupled to the current transfer portion to form a second temperature sensing junction, wherein the second temperature sensing junction is spaced apart from the first temperature sensing junction. The first and second temperature sensing junctions are thermally coupled to the first and second temperature generating junctions respectively. The first temperature sensing junction is cooled to at least a portion of the temperature of the first temperature generating junction and the second temperature sensing junction is heated to at least a portion of the temperature at the second temperature generating junction. The first thermal difference generator senses the temperature difference between the first and second locations and provides an output signal that is a function of the temperature difference between the first and second temperature sensing junctions.
The current sensor further includes a dielectric barrier interposed between the first thermal difference generator and the first thermal difference sensor located.
Other forms, features, and aspects of the above-described methods and system are described in the detailed description that follows.